The document U.S. Pat. No. 7,282,005 B2 discloses a hydraulic system for actuating a shifting element of a transmission having a regulating valve device, which can be preset and has a regulating valve slide, and a shifting valve device, which is in effective connection thereto, and also can be preset, as well as being formed having a shifting valve slide. The pilot pressure for the regulating valve device and the shifting valve device is preset by a pressure regulating device depending on an electrical control signal, wherein the pressure regulating device has a defined working pressure range that is typically significantly lower than the actuating pressure of the shifting element. In order to be able to actuate the shifting element with higher pressure values compared to the pilot pressure of the regulating valve device and the shifting valve device, the regulating valve device is connected downstream of the pressure regulating device, in the region in which the pilot pressure of the pressure regulating device is converted to a higher level.
In general, during driving operation of a vehicle that is implemented having a transmission such as a torque-converter transmission or the like, it should be guaranteed that the shifting element in the completely engaged operating state is operated slip-free and has the full transfer capability thereof. For this purpose, the actuating pressure at the end of the regulating pressure range of the actuating pressure is increased step-like to a higher pressure value that corresponds to a so-called system pressure. The changeover, or the at least nearly step-like increase of the actuating pressure is implemented via the shifting valve device controlled in parallel by the pressure regulating device; the shifting valve device, however, is actuated, or transferred, out of a first shift state into a second shift state only at high pilot pressures.
The feedback from the actuating pressure to the regulating valve device is deactivated via the shifting valve device upon presence of a second shift state of the shifting valve device, so that the regulating valve device is transferred out of a so-called modulation position into an operating state, in which the system pressure present at the regulating valve device is completely passed through in the direction of the shifting element.
Because a regulating valve slide of the regulating valve device and a shifting valve slide of the shifting valve device are respectively disposed in separate valve borings, a hydraulic system formed in such a manner has an undesirably high construction space requirement.